Traffic Light Sensors: How Traffic Lights Go From Red to Green

By Anthony K

How long does it take for traffic lights to change from green to red or vice versa? The short answer is that it may depend on your driving skills and the type of sensors.

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Traffic lights may operate on a timer, digital sensors, or induction loops. Depending on the sensor, the time may be rather short or rather long. Read on to discover why you take longer at some traffic lights and how to make inductive loop systems work in your favor.

Inductive Loop Systems

Inductive loops detect changes in inductance by constantly testing the loop’s inductance to detect whether a car is waiting. Lighter motorcycles and vehicles may not trigger the inductor and could make you wait much longer when the traffic is low.

A driver should pull up to a stop section to trigger the induction coil for traffic lights to change.

Infrared Sensors

Infrared sensors are available in passive and active variations. Active infrared sensors shoot out beams of infrared lights stopping where a car may stop during a red light. A car breaks the beam allowing the sensor to detect the occupation and change the lights.

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Passive sensors use infrared sensors to detect heat from a car’s engine to change the traffic lights.

Video Camera Systems

Video cameras are complex but have proven quite effective. The cameras are installed on traffic lights, similar to CCTV cameras, and are networked to work effectively.

They are connected to a server running software identifying, counting, and distinguishing cars from pedestrians. Bad weather, like fog, can limit the camera’s vision, which can delay the light change.

Microwave Sensors

A microwave sensor generates a magnetic field around itself. A vehicle entering the zone disturbs the magnetic field prompting it to change the waves allowing the sensor to detect changes and see the car.

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Microwave emitters reduce errors emanating from heat contamination of infrared sensors that could misinterpret heat on hot days.